a) Field of the Invention
The present invention relates to a valve device in which a valve element is operated to perform opening/closing of a flow path for various types of fluid. More specifically, the present invention relates to a valve element opening/closing mechanism for a valve device.
b) Description of the Related Art
A valve device has been known which performs a temperature control in a chamber which is in communication with a flow path by means of opening or closing the flow path for various types of fluid such as refrigerant for a refrigerator or an air conditioner. An inflow pipe for allowing the fluid to flow in and an outflow pipe allowing the fluid to flow out are connected to the valve device. The valve device includes a main body case within which a fluid flow path is constructed for guiding the fluid flowing from the inflow pipe to the outflow pipe, a valve element disposed on an inner side of the main body case for opening or closing an outflow aperture part of the main body case which is in communication with the outflow pipe, and a valve element drive means having a motor drive part for opening or closing the valve element.
One of the valve devices utilizes a so-called disk type of valve element opening/closing mechanism. In the disk type of valve element opening/closing mechanism, an outflow aperture part provided in a main body case is opened or closed by means that a disk-shaped valve element provided with a sliding face is rotationally slid on the valve seat plate of the main body case provided with the outflow aperture part by a valve element drive means with the rotation torque of the motor drive part through gears (for example, see Japanese Patent Laid-Open No. 2003-21254). Further, a so-called ball type of valve element opening/closing mechanism has been also used in which an outflow aperture part is opened or closed by a valve element drive means such that a spherical valve element urged against an outflow aperture part is moved by a cam provided on a rotary member driven by a motor (for example, Japanese Patent Laid-Open No. 2002-349741).
However, in the disk type of valve element opening/closing mechanism, a disk-shaped valve element is commonly formed of resin and a valve seat plate is formed of metal such as stainless steel to construct a sliding face between the valve element and the valve seat plate. Therefore, sliding resistance between the valve element and the valve seat plate varies depending on the degree of the surface roughness or the flatness of the sliding face and thus the torque required in the motor drive part also varies at a starting time or at an opening/closing operation time. Further, the sliding resistance increases due to the aged deterioration of the sliding face and therefore the required torque of the motor drive part increases at a starting time or at an opening/closing operation time. Accordingly, the stable opening/closing control of the valve element becomes difficult.
Also, in the ball type of valve element opening/closing mechanism, the spherical valve element is pressure contacted with the outflow aperture part by fluid pressure. Therefore, when the cam moves the valve element, the rotating torque larger than the fluid pressure is required in the motor drive part. Accordingly, when the fluid pressure varies, the contact resistance between the cam and the valve element varies and thus required torque of the motor drive part also varies. Especially when the fluid pressure is high, the required torque of the motor drive part increases and therefore, a stable opening/closing control of the valve element becomes difficult unless a motor drive part with a large rotating torque is used.